We have isolated, via differential hybridization screening of a floral cDNA library from sunflower, a cDNA clone that hybridizes to a 1100 nucleotide-long mRNA found exclusively in mature pollen grains. The cDNA encodes a 219 amino acid-long polypeptide containing two potential zinc fingers alternating with two basic domains. A similar organization is found in the erythroid-specific transcription factor Eryf1 from chicken and its murine homolog GF-1. The C-terminus of the protein contains a sixfold repeat of the pentapeptide sequence (S,T,A)(E,D)TQN. These features suggest that the SF3 protein is a transcription factor required for the expression of late pollen genes. The SF3 gene is a member of a multicopy gene family. A genomic copy of the gene has been isolated and sequenced; it is split by four short, AT-rich introns.